In vivo pharmacokinetic study in rats

In vivo pharmacokinetic study in rats was conducted to confirm the optimized conditions established in vitro using Sprague Dawley (SD) rats. The SD rats (270–300 g) were purchased from Daehan Laboratory Animal Research Co. (Chungbuk, Korea), allowed free access to normal standard rodent diet (Jaeil Chow, Korea) and tap water. The animals were housed individually in laminar flow cages at 22 ± 2℃, and 50–60% relative humidity and stabilized in these facilities for at least 7 days before experiments in vivo. Procedures were approved by the Animal Care Committee of Chungnam National University. For percutaneous administration, the hair was removed from the skin of the dorsal region using electric hair clippers. The vitamin C gel alone was applied to the rat skin as a control. The vitamin C gel was loaded onto the shaved surface rat skin after applying the vibrating microneedles with the optimized conditions established by in vivo pharmacokinetic study in rats. Vibrating microneedles with vibration intensity of level 3, application power of 1,000 g and application of 5 min were pretreated for the transdermal administration of 0.5 g of the vitamin C gel (27.5 mg/kg of vitamin C). The application area was covered with a thin plastic film and fastened around the edges with adhesive tape to avoid loss of gel. Blood samples (about 1 mL) were collected at 0.5, 1, 2, 4, 8, 12, 24 and 72 h after percutaneous administration from the retro-orbital plexus using disposable capillary tubes that were prerinsed with heparin sodium in normal saline (20 IU). The collected blood samples were centrifuged at 11310 g for 10 min to obtain plasma, which was stored at −70℃ until analysis by HPLC.